This application is a continuation of copending U.S. application Ser. No. 14/645,991, filed on Mar. 12, 2015 which is incorporated herein by reference.
1. Field of the Invention
One embodiment of the present invention relates to a light-emitting element in which an organic compound capable of providing light emission by application of an electric field is provided between a pair of electrodes, and also relates to a light-emitting device, an electronic device, and a lighting device including such a light-emitting element.
Note that one embodiment of the present invention is not limited to the above technical field. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a method for driving any of them, and a method for manufacturing any of them.
2. Description of the Related Art
As next generation lighting devices or display devices, display devices using light-emitting elements (organic EL elements) in which organic compounds are used as light-emitting substances have been developed and partially commercialized because of their potential for thinness, lightness, high speed response to input signals, low power consumption, and the like.
In a light-emitting element, voltage application between electrodes between which a light-emitting layer is provided causes recombination of electrons and holes injected from the electrodes, which leads a light-emitting substance that is an organic compound to an excited state, and the return from the excited state to the ground state is accompanied by light emission. Since the spectrum of light emitted from a light-emitting substance is peculiar to the light-emitting substance, use of different types of organic compounds for light-emitting substances makes it possible to provide light-emitting elements which exhibit various colors.
In the case of light-emitting devices which are expected to display images, such as displays, at least three-color light, i.e., red light, green light, and blue light, is necessary for reproduction of full-color images. Further, to enhance image quality with favorable color reproducibility, various efforts such as use of a microcavity structure and a color filter (coloring layer) have been made to improve color purity.
A light-emitting device with lower power consumption due to addition of white light to three-color light (red light, green light, and blue light) has been proposed and commercialized.
There are mainly three methods to realize full-color display using the light-emitting elements described above: so-called side-by-side patterning in which light-emitting elements which emit light of different colors are separately formed; a white-color filter method in which a white-emissive light-emitting element is combined with a color filter; and a color conversion method in which a monochromatic light-emitting element such as a blue-emissive light-emitting element is combined with a color conversion filter. Each of the methods has advantages and disadvantages.